FIG. 1 is a flow chart illustrating a conventional call processing for providing a video call over WCDMA based mobile communication network using the 3G.324M protocol.
When an Originating Mobile Station, MSO 10, makes a video call to a Target Mobile Station, MST 50, a Setup message for call origination to enable the video call using the 3G.324M protocol is sent from the MSO 10 to an Originating Mobile Switching Center, MSCO 20 (S110). Within the Setup message, an Information Transfer Capability (ITC) value of the call is set to Unrestricted Digital Information (UDI) so as to enable the transfer of digital data, and an Other Rate Adaptation (ORA) field is set to the 3G.324M protocol. The 3G.324M protocol comprises H.223 protocol, a standard for multiplexing multimedia data, and H.245 protocol, a standard for system control.
Next, the MSCO 20 replies to the MSO 10 with a Call Proceeding message informing that it will proceed with the call (S112).
Moreover, in order to get the location information of the MST 50 and connect the call thereto, the MSCO 20 sends a Send Routing Information (SRI) request to a home location register (HLR) 30 (S120).
In response to the SRI request, the HLR 30 sends a Provide Roaming Number (PRN) request to a Target Mobile Switching Center, MSCT 40, which the MST 50 is connected to (S122).
As a response to the PRN request, the MSCT 40 transmits PRN information to the HLR 30 (S124). And as a response to the SRI request, the HLR 30 transmits SRI information, which is acquired from the PRN information, to the MSCO 20 (S126).
Then, the MSCO 20 finds out the location of the MST 50 through the SRI information and transmits an initial address message (IAM) including ID information of the MST, such as a telephone number, to the MSCT 40 which the MST 50 is connected to (S130). The IAM message requests the MSCT 40 to establish a circuit connection to reach the MST 50.
Next, the MSCT 40 sends a Paging message to the MST 50 in accordance with the IAM (S150), and the MST 50 sends a Paging Response to the MSCT 40 (S152).
Afterwards, the MSCT 40 sends a Setup message to the MST 50 (S160), and the MST 50 sends the MSCT 40 a Call Confirmed message as a response (S162), followed by an Alert message (S170). In this manner, a traffic channel is established between the MST 50 and MSCT 40.
Meanwhile, in response to the IAM message, the MSCT 40 sends the MSCO 20 an address complete message (ACM) indicating the acquisition of the MST ID (S178), and the MSCO 20 sends the MSO 10 an Alert message for informing such (S179).
When the MST 50 answers or receives the call in response to a call-incoming or ringing, it delivers a Connect message to the MSCT 40 (S180), and receives a Connect Ack message (S182).
In the meanwhile, after receiving the Connect message from the MST 50, the MSCT 40 transmits an answer message (ANM) to the MSCO 20 (S184). Then, the MSCO 20 sends a Connect message to the MSO 10 (S186) and receives a Connect Ack message (S188).
In this manner, a call is connected between the MSO 10 and the MST 50, and then a negotiation for video and audio channel setup and the like according to the H.245 protocol is made (S190), and audio and video data are transmitted by the H.223 protocol (S192).
However, in mobile communication services using the above way, an audio or video multimedia signal can only be sent to the called party, MST 50, after the traffic channel is built between the MSO 10 and the MST 50 (S170 through S179) and the called party receives the call (S180).
In other words, the conventional technology is not able to provide multimedia service while the MST is still ringing.